REPRODUCTIVE AND RENAL ORGANS 37 



figured the spermatozoa of many birds, whence it appears that 

 their form is often characteristic, and may be of systematic 

 use. A penis is not present in all birds ; it exists in the 

 Struthiones, the Anseres, Tinami, Herodioues, Galli, and 

 (Edicnemus. Tt is a paired organ — that is to say, it is 

 composed of two incompletely joined halves with a longi- 

 tudinal groove. 



The Coelom 



Birds differ both from reptiles and mammals in the com- 

 plication of the subdivisions of their body cavity. The 

 subject is one that is far from being thoroughly worked out, 

 but enough information has been collected to allow of a 

 certain amount of definite statement and of comparison 

 with other animals. 



When a bird is dissected in the usual way from th6 

 ventral surface, the abdominal cavity, or at least the cavity 

 containing what are generally termed the abdominal viscera — 

 i.e. liver, intestines, &c. — is seen to be divided into two by a 

 toughish septum, which varies in extent according to the 

 bird dissected. This membrane, to which attention has 

 been directed by Wbldon ' under the name of ' pseudepi- 

 ploon,' has been investigated in a number of birds by me.^ 

 Its relations in the common fowl have been described with 

 the aid of diagrammatic representations of sections by 

 Butler.' 



This membrane, believed by Mall"" to be the actual 

 homologue of the omentum of the mammal, is more or less 

 horizontal in direction, so that it may be conveniently 

 termed, without prejudice to its homologies, the ' horizontal 

 septum.' This horizontal septum is attached to the ventral 

 body wall, to the oblique septa (of which see description 

 later), and to the gizzard, which viscus appears to lie within 



' In his memoir upon the anatomy of the storks and flamingo in P. Z. S. 

 1883, p. 638. 



' ' Notes on the Visceral Anatomy of Birds,' P. Z. g. 1885, p. 836. 



' ' On the Subdivision of the Body Cavity in Lizards, Crocodiles, and Birds,' 

 P. Z. S. 1889, p. 452. 



' Journ. Morph. 1891. 



